The purpose of this project is to determine the specific immune mechanisms responsible for host defense against influenza. We are particularly interested in the role of cell mediated immunity, systemic and local antibody in the prevention of and recovery from both influenza rhinotracheitis and pneumonia. We are also interested in the role of specific immune mechanisms in the pathogenesis of both alveolar and airway disease. The basic approach is to selectively transfer a component of the immune system and test whether that transfers the ability to prevent influenza rhinotracheitis or pneumonia or enhances recovery to either of these processes. Alternatively we will selectively ablate one component of the immune system and see if this interferes with some aspect of protection against influenza. We also propose to use the ontogeny of the immune system to help define host defense against influenza.